Circuit interrupter



Patented Feb. vl5, 1938 CIRCUIT INTERRUPTER Herbert L. Rawlins, Wilkinsburg, Pa., asslgnor to Westinghouse Electric & Manufacturing Company, East Pittsburgh, Pa., a corporation of Pennsylvania Application March 30,

30 Claims.

My invention relates to circuit interrupters and particularly to high voltage circuit breakers of the type which utilizes an expulsive gas blast for extinguishing the arc formed incident to the interruption ofthe controlled circuit.

Expulsion circuit breakers usually comprise a tubular arc passage, a means, such as a fuse or a movable plunger, for drawing an arc within the tubular arc passage, and a means for producing an expulsive gas blast which flows longitudinally through the arc to eilect its extinguishment. The eiliciencyl and the reliability of operation of these devices dependA to a great extent upon the amount and the chemical characteristics of the gas which is caused to expulsively ow through the arc during the circuit interrupting operation, and the principal problem of the art has always been the securing of an adequate volume of gas having a satisfactory chemical composition.

The most satisfactory structure so far evolved, secures the desired longitudinal blast of arc extinguishing gas by lining the arc passage. with an insulating material which is capable of evolving large quantities of arc extinguishing gas and whichvdoes not lose its insulating properties when placed in proximity to an electric arc. Preferably, the gas is inorganic in nature, readily condensable, and non-inammable. All offthese requirements are met by a lining composed of compressed boric acid, but, even this arrangement has not proved entirely free from defects.

'I'he evolution of gas from the surface of the lining of the arc passage depends to a great extent upon the intimacy of contact between the 27' lining and the arc, and it is obvious that the maximum possible evolution of gas (and the most efiicient operation of the interrupter) willv be effected when the arc completely fills the arc passage. Unfortunately, however, the magnitude of the overload current on most present day circuits may vary through wide limits,` and the physical dimensions of the are likewise vary in direct proportion. It might appear that this would not create any serious diiliculties, since the arc passage could be made small enough to cause an intimate engagement between the lining and the surface of the smallest magnitude arc that might be drawn within the arc passage.

The problem is not so simply solved, because. while intimate engagement between the lining of the arc passage andthe arc is imperative, it is possible to have an arc passage which is too small. If this occurs and large magnitude arcs are drawn therein the volume of gas generated may be sutil-A ciently large to cause a rupture of the walls of 1934, Serial N0. 718,267

(Cl. 20o-117) the are passage, and even if the walls of the passage are not ruptured, the surfaces of those walls which are exposed to the arc may be heated suffi-v ciently to become conducting and thereby make the interruption of the controlled circuit impossible.

This possibility 'of actual destruction of the circuit interrupter, or failure of the device to operate, during the occurrence of very heavy overload conditions, makes it necessary that the physical dimensions of the arc passage shall be suiiiciently large to permit an arc having the largest possible current magnitude, for the circuit on which the device is to be used, to be drawn within the arc passage without danger of rupture or excessive heating. The obvious resultoi this is that for most circuits the arc passage" must have a very considerable cross-sectional area, and when the interrupter is in use on such circuits, the low magnitude arcs produced by normal overloads will but partially iill the arc passage. Under these conditions, only a small volume of arc extinguishing gas will be generated, and the eillciency of the interrupter will be very low. In fact, if the current magnitude of the arc'is very small, it may be impossible to extinguish it at all.

To overcome this diiiiculty, the prior art structures have utilized two arc passages, one of large cross-sectional area wherein arcs of heavy current magnitudes are interrupted, and one of small cross-sectional area wherein arcs of a lower current magnitude are extinguished. This arrangement requires selective means for assuring that the arc shall be drawn in the proper passage, and is not entirely satisfactory from an economic viewpoint.

The principal object of my invention is, therefore, to provide an improved expulsion circuit interrupter, of the type discussed above, that shall utilize but a single arc passage and that shall be provided with means for assuring the satisfactory interruption of both small and large current arcs inthat passage.

In carrying out the principal object of my invention, I provide a suitable means for defining an arc passage, a plunger for drawing an arc within that passage, and a means of insulating material, which preferably forms a part of the plunger, movable into the arc passage only when arcs of small current magnitude have been or are being drawn thereon. This means of insulating material restricts the cross-sectional area of the arc passage in such manner that even the low magnitude arcs are brought into intimate contact with the'lining of the passage and as a result a suilicient volume of arc extinguishing gas will be evolved to assure a rapid and complete extinguishment of the arc. 4

A further object of my invention is to provide an expulsion type circuit interrupter with means for introducing a body of insulating material, itself capable of evolving an arc extinguishing gas `when placed in proximity to an electric arc, into the varc passage thereof during the circuit opening operation.

Since, as pointed out above, the principal'eld for immediate application of my invention is in connection with expulsion circuit breakers ofthe plunger type, I shall hereinafter describe an embodiment of my invention as applied to such devices, without,'however, in any way intending to restrict the scope of my invention except as indicated in the appended claims.

Referring to the single sheet of drawing:

Figure 1 is a sectional view, partially in elevation, of an expulsion type circuit interrupter embodying the principal featuresof my invention;

Fig. 2 is a sectional view taken on the line II--II of Fig. l; and

Fig.l 3 is a fragmentary detailed view, partially in section, showing a mndiiied form of plunger for use with the circuit interrupter shown in Figs. 1 and 2.

The expulsion circuit interrupter; shown in the drawing comprises, generally, a tube I of insulating material, which possesses suicient strength to withstand the pressures ordinarily developed within these devices, a metallic cap or ierrule 3 for enclosing the upper end of the main insulating tube I, and a second ferrule 5, having a centrally disposed opening 1 therein, for engaging the lower end of the insulating tube. Both the` upper and lower ferrules are adapted to be retained in position by means of suitable screw threads Sand II formed in the cooperating portions of those members and the tube I. A tubular member I3, of conducting material, having a threaded portion I5 at one end, which portion engages a similarly threaded portion I 1 forming a part of the upper ferrule 3, is disposed within the main tube I, 'both for the purpose of reenforcing the tube and for completing the electrical circuit from. the upper ferrule to the annular plate I9 positioned beneath the lower end of the tubular member I3.v

A cylindrical member 2|, preferably o f compressed boric acid or other gas generating ma.- terial, having ay centrally disposed passage 23 therein is positioned within the lower portion of the main tube'v I. The passage 23 constitutes the arc passage, the arc being established therein by the movable plunger assemblage 25. The boric acid .member 2ll is retained in position within the main tube I by the annular plateJIS, which engages the lower portion of the conducting tube I3, andthe lower ferrule 5. The open- -ing 21 in the annular plate I9 is of substantially the same dimensions as the arc passage 23, and that passage terminates in a funnel-shaped opening 29, the-largest diameter of which is substantially the same as thel opening 1 in the lower `ferrule 5.

The plunger assemblage 25 -comprises generally a rod or plunger having a conductingportion 3| for drawing the arc into` the arc passage 23, an insulating portion 33 for limiting the crosssectional area of the arc passage,l an electro-responsive mechanical connection between the conmeans through the arc passage. T'he conducting portion 3| comprises a circular rod of conducting material, the upper end 35 of which is threaded for engagement with a suitable threaded opening in the movable piston member 31. The piston member 31 is circular in outline and is of somewhat smaller diameter than the tubular conducting member I3 wherein it is adapted to move. The lower end of the conducting portion 3I of the plunger is provided with a section 39 of reduced cross sectional area. This reduced section is threaded for engaging the upper end of the insulating portion 33 and serves to provide an electro-responsive mechanical connection between the two portions of the plunger. The piston member 31 and with it the two mechanically connected portions of the plunger proper are biased in the direction of the upper ferrule, at all times, by a coil spring 4I. Movement in this direction is prevented by a fusible element 43, one end of which fits within a suitable recess 45 in the upper or cap portion 41 of the insulating portion of the plunger, and the other end of which ts Within a like recess' 49 in the lower ferrule 5.

The insulating portion 33 of the plunger may be formed of a number of different materials. If the interrupter is to be used out of doors, it may be desirable to form that member of a ceramic material or other which will not absorb moisture. If the device is to be used indoors, the rod may be formed of fiber or other materials more or less hydroscopic. In either case the material should be capable of retaining its insulating properties when placed in proximity to an electric arc.

For certain applications, it may be desirable -to form the insulating portion 33 of material which is capable of evolving an arc extinguishingl gas when brought into proximity with an electric arc, this arrangement being particularly suitable for use on circuits wherein it is desirable to have the minimum possible arcing time. If boric acid .or other structurally weak materials are used for this purpose, it is desirable to reen'- force the plunger, and a structure of this type is shown in Fig. 1.'` The insulating portion 33 of the device shown in that figure is formed of a material which is structurally weak, and a tubular reenforcing member 5I is molded or formed integral therewith. This reenforcing member 5I is provided with a threaded portion 53 at its upper, end, for engaging a cooperating threaded recess in metallic top or cap portion 41 of the insulating member- 33. g

This cap portion 41 is also provided with a second threaded. recess 55 for engaging the threaded end of the reduced section 39 of the conducting portion 3| of the plunger. 'Ihis recess 55 connects with the recess 45, which is provided for the reception of one end of the fusible element 43, and when the device is completely assembled the threaded end of the section 39 is screwed down ontothe end of the fusible element 43 in .order .to complete the electrical circuit from thev conducting portion 3| -to the fusible element 43 and to mechanically connect the fusible element with the plunger.

The modified form of the insulating portion of the plunger illustrated in Fig. 31s adapted for use with insulating materials having a suillcient mechanical'strength to obviate the necessity for reenforcing the insulating portion 33 of the plunger or for providing a cap means. When such materials are used, the upper end of the insulating rod/51 may be:e provided with a recess 59 for engaging one end of the fusible element I3 and a threaded opening 6I for engaging the cooperating threaded end of the conducting rod The electrical circuit through the fuse is comparatively direct. Beginning with the upper ferrule 3, the current flows successively through the tubular conducting member I3, the annular plate I9, the flexible shunt 63 intermediate the annular plate I9 and the pistonmember 31, thence through the piston member 31 and the conductingportion 3| of the plunger 25 to the fusible element 43, and through that element to the other ferrule 5.

Upon the occurrence of a predetermined moderate overload in the circuit controlled byl the device, the fusible element 43 melts, thereby releasing the plunger and allowingl that member to be moved to the open-circuit position under the biasing action of the spring 4I. The conducting portion 3I of the plunger, by virtue of this movement draws the arc into the arc passage 23 and at the' same time causes the entry of the insulating portion 33 of the plunger into that passage. The insulating portion v33 restricts the cross-sectional area of the arc passage and brings the arc into intimate contact with the surface of 'the boric acid lining 2|. A considerable amount of water vapor is evolved as a result of this intimate contact, and since the only way that this vapor can vent is through the opening in the lower ferrule 5, a. rapidly outfiowing blast oi' arc extinguishing gas is produced which usually causes the interruption of the arc within a few half cycles. i

While as mentioned above it is necessary that the arc be brought into intimate contact with the .gas evolving lining of the arc passage in order to secure satisfactory operation of the interrupter, it has been found that thedimensions of the several parts are not very critical. Y This results from the fact that on the ordinary circuits in use'at the present time, overloads usually fall within two general classes. The first of these classes includes the normal overloads resulting.

from excessive loading of the protected equipment, and their magnitude lrarely exceeds the normal full load current by more than a few hundred percent. The other class of overloads are those resulting from short-circuit or linefault conditions, and these are ordinarily of very large magnitude-several thousand percent of the normalfull load current. Thus, if the arc passage and the mea'ns for limiting the area thereof are so designed that satisfactory interruption of the circuit can be secured for the usual range of normal overload values, and if a means is provided for'taking care of the very large overload which results from short circuits or the like, it is extremely improbable that the interrupter will notsuccessfully operate under all possible conditions. This, in effect, is what is done with my improved type of circuit interrupter, which normallyl has a small arc passage for interrupting the usual overload currents, and

which is provided with electro-responsive means `for increasing the area of the arc passage in order to successfully interrupt -short circuits or 'very heavy overload currents.

ment 43 melts, thereby releasing the plunger, that member then being moved .under the action of the biasing spring 4| to establish the arc within the are passage 23.l However, due to the fact that the cross-section area of the section 39 of the conducting .portion 3| of the plunger, which section is used for mechanically connecting the conducting portion and the insulating portion of the plunger is of restricted cross-sectional area, considerable heating will occur at that point. If the magnitude of the arc current is sufllciently high this heating will result in the fusion of the section 39 of the conducting memto be 'disconnected from the arc drawing portion 3| of the plunger before the upper end of the insulating portion has been drawn into the.

arc passage. Should this occur, when a very large volume of gas is being generated within the arc passage 3|, a very considerable force will exist upon the insulating portion 33 of the plunger, tending to move it out of the arc passage, and before the pressure within the arc passage reaches a`dangerous magnitude, the insulating portion 33 will be forcibly ejected from that passage. The point of fusion of the mechanical connection between the conducting and insulating portions of the plunger should be, of course, properly adjusted, taking into consideration the characteristics of the lcircuit wherein the device is to be used and the interrupting capacity of the arc passage.

From'the foregoing it will be seen that I have provided an improved expulsion type circuit interrupter which is capable of satisfactorily interrupting arcs of small and of large magnitude Within a single arc passage, this arrangement differing from the prior art devices which utito cause the insulating portion 33 of the plunger adapted for use in conjunction with my invention.

While in accordance with the patent Statutes I have disclosed the foregoing details of a praction shall be given the broadest reasonable con-1 struction, and that the claims shall' be limited only by what is expressly stated therein, and by the prior art.

I claim as my invention:

1.' In an expulsion circuit interrupter, means,

defining a tubular passage substantially closed at one end, means, of'a material capable of evolving' an arc extinguishing gas when placed in proximity to an electric arc, lining at least a part of said passage, means movable longitudinally in said passage to establish an arc therein, and means of insulating material, havinga v cross sectional area at least slightly less than the tion in order to retrict the cross-sectional area of the arc so as to effect an intimate engagement between the arc and a substantial portion of the gas evolving portion of said lining.

2. In an expulsion circuit interrupter, means defining an arc passage, means for producing a blast of gas which flows expulsively through said passage during each'opening operation of said interrupter to extinguish the arc incident to such operation, and a plunger movable through said passage during the circuit opening operation, saidplunger having a portion of conducting material for establishing said arc within said passage, and a portion of insulating material of less cross sectional area than said passage for limiting the cross-sectional area of at least a portion of said passage during the operation of said interrupter.

3. In an expulsion circuit interrupter, means deilning a passage having substantially rigid walls, at least a portion of said passage being lined with a material capable of evolving an arc extinguishing gas when placed in proximity to an electric arc, means for establishing an arc With-y in said passage, said passage having an opening for the escape of gas therefrom, means of insulating material movable into said passage, said movable means having a cross sectional area appreciably less than the cross sectional area oi said arc passage, and means operable when but only when the magnitude of the current iiovving` through said arc is less than a predetermined value to cause said -means of insulating material to enter at least a portion oi' said passage in order to eiect a more intimate engagement between the arc and the gas evolving portion of said lining.

4. In a circuit interrupter for use with circuits subjected to overloads of widely `-varying magnitude, means defining a tubular passage at least a portion of which is lined with a material capable of evolving Aan arc extinguishing gas, when placed in proximity to an electric arc, means for establishing an arc within said passage, said passage having a vent for the escape of gas therefrom, and means, responsive to the magnitude of the current ilowing in the circuitl controlled by said interrupter, for controlling the cross-sectional area of at least a portion of said arc in order to effectively extinguish arcs of both large and small current magnitude.

5. In an expulsion circuit interrupter, means dening a tubular passage that is substantially closed at one end and open at the other, means of a material capable of evolving an arc extin Aguishi'ng gas and capable of retaining its insusage, and means operable when but only when the magnitude of the current flowing through said arc is less than a predetermined value to cause said means of insulating material to enter said passage and to move through at least a portion thereof so as to restrict the volume of said passage in order to'eect a more intimate engagement between said arc and the gas evolving portion of said lining.

6. In a circuit interrupter, means deiining a passage, a plunger, and means for moving said plunger through said passage, during the circuit interrupting operation, said plunger having a portion of conducting material for establishing an arc within said passage and a portion of insulating material which, when moved into said passage, limits the cross-sectional arca of` at least a portion thereof, said portion of insulating material being mechanically connected to said arc drawing portion by means operablewhen the current flowing through said interruptor exceeds a predetermined value to mechanically disconnect said portion of insulating material from said arc drawing portion.

7. In a circuit interrupter, means defining a tubular passage at least a portion of which' is lined with a material capable of evolving an arc extinguishing gas when placed in proximity to an electric arc, a plunger, and means operable upon the occurrence of predetermined conditions to move said plunger through said passage, said plunger including a portion of conducting material for establishing an arc within said passage and a portion of insulating material which, when moved into said passage, limits the cross-sectional area of at least a portion of said passage so as to ciicct an intimate engagement between said arc and said gas evolving portion of said lining, said portion of insulating material being mechanically connected to said arc drawing portion by means operable when the current flowing through said interruptor exceeds a predetermined value to mechanically disconnect said portion of insulating material from said arc drawing portion.

8. In ai circuit interrupter for use with circuits `subjected t-o overloads of widely varying magnitude, means dening a tubular passage at least a portion of which is lined with boric acid, means for establishing an arc within said passage, means for vent-ing said passage, and means, responsive to the magnitude of the current flowing in the circuit controlled by said interrupter, for controlling the cross-sectionalarea of at least a portion of said passage wherein said arc is established in order to effectively extinguish arcs of both large and small current magnitude.

9. In acircuit interrupter, means defining a passage, a plunger, and means for moving said plunger through said passage, during the circuit interrupting operation, said plunger vhaving a portion of conducting material for establishing an arc within said passage and a portion of insulating material which is capable of evolving an arc extinguishing gas, and which retains its insulating properties, when placed in proximity to an electric arc, said portion of insulating material, when lmoved 'into said passage serving to limit the cross sectional area `oi at leastl a portion of said passage, said portion of insulating material being mechanically connected to said arc drawing portion by means operable when the current-ilowing through said interrupter exceeds a predetermined value to mechanically disconnect said portion of insulating material -from said arc drawing portion.

l0. In lan expulsion circuit interrupter, rigid mean-s for defining the walls of an arc passage having a length at least several times its greatest Width, means for establishing the arc incident to the opening of said interruptor within said arcpassage, means for producing an expulsive blast of gas through said passage for extinguishing said arc, and means for introducing a solid member of insulating material into said arc pas- H 2,108,550 sage during the circuit opening operation, said member being of less cross sectional area than said arc passage in order that while it shall substantially restrict the area of said arc passage, so as to effect intimate engagement between said arc and the surfaces of said wail ldefining means and 'said member, it shall not ll. In a ,circuit interrupter, rigid means for defining the walls of an arc passage having a length at least several times its greatest width,

at least a portion 'of said passage being lined wit-h a material capable of evolvingan arc extinguishing gas when placed in proximity to an electric arc, means for closing one end of said arc passage, -the other end of said passage being open, at least during the circuit opening opera'- tion, means for establishing the arc incident to the opening of said interrupter within said arc passage, and means for introducing a solid member of insulating material into said arc passage during the circuit opening operation, said member being of less cross sectional area than said `arc passage in order that while it shall substantially restrict the area of said arc passage, so as to eiect intimate engagement between said arc and thesurfaces of said wall defining means and said member, it shall not, by its entry thereinto, entirely close said passage.

l2. In an expulsion circuit interrupter, rigid means for defining the walls of a substantially the diameter oi said movable member being apcylindrical arc passage having a length at least several timesits width, at least a portion of said larcpassage being lined -with a material capable .of evolving an are extinguishing gas when placed in-proximity to an electric arc, means for closing one end of said -arc passage during each circuit opening operation,'the other end of said arc passage being open during each circuit opening operation, means for establishing the arc incident to the opening of said interrupter within said arc passage, and vmeans for moving a solid member.

of insulating material having a substantially cylindrical outer surface' into said varc passage, in such manner that it is substantially concentric therewith, during the circuit opening operation,

preciably less than the diameter of said arc passage in order that the movement of said member thereinto shall eii'ect a substantial restriction of the area of 'said arc passage, so as to effect intimate engagement between said arc and the opposed concentric surfaces of said wall defining means and said memberfwithout entirely closing said arc passage. i

.13. In an expulsion circuit interrupter, means for defining the walls of an arc passage, means :to effect .intimate engagement between said arc and the surfaces of said wall dening means and said member and Ato permit the flow oi said blast 'of'gssbetw'een said wall defining means and said member.

14. In an expulsion circuit interrupter, means for defining the walls of an arc passage, at least a portion of said means being formed of an insulating material which is capable of evolving an arc extinguishing gas when placed in proximity to an electric arc, means including a fusible ,element for establishing the arc vincident to each opening operation of said interrupter within said arc passage, and means for introducing a solid member of insulating material into said arc passage during the circuit opening operation of said interrupter, said member being so proportioned that it shall substantially restrict the cross sectional area of said arc passage to effect intimate engagement between said arc and the surfaces of said wall dening means and said member and to permit the flow through said arc passage of the gas evolved from said insulating material.

15. In an expulsion circuit interrupter, rigid means .having a substantially .cylindrical passageway formed therein for dening the Walls of an arc passage, means for establishing the arc incident to the opening of said interrupter within said arc passage, means for producing an expulsive blast of arc extinguishing gas' which ows longitudinally through said arc passage during the opening operation of said interrupter for extinguishing said are, said passage having an opening to permit the escape of gas therefrom,A

at least partially of insulating material and being so proportioned that it substantially restricts the area of said arc passage to effect intimate engagement between saidlarc and the opposed surfaces of said wall defining means and said member and 'to perrnitthel flow of said blast of arc extinguishing gas through said opening.

16. In an expulsion circuitinterrupterior use with circuits subjected to overloads of Widely varying magnitude, rigid tubular means for de- `iining the walls of an arc passage having a length at least several times its greatest width, means for establishing thevarc incident to the opening of said interrupter within said arc passage, means for producing an expulsive blast of gas which ows longitudinally through said arc passage during the circuit opening operation of said interrupter for extinguishing said arc, said passage having a vent to enable the blast of gas to escape therefrom, and means responsive to the magnitude .of the current owing in the circuit controlled by said `interrupter for controlling the cross-sectional area of at least a portion of said arc passage in order thatI said blast of gas shall effectively extinguish arcs of both large and small current magnitude.

1'7. In an expulsion circuit interrupter, means for deiining the walls of an arc passage, at least a portion of said wall deiining means being formed of an insulating material which is capable of evolving an arc extinguishing gas when placed in proximity to an electric arc, and a plunger movable through said arc passage during the operation of said interrupter, said plunger having a portion of conducting material for establishing the arc incident to each opening operation of said interrupter within said passage and a portion of insulating material ofless cross-sectional area than said passage for restricting the cross-secengagement between said arc and the inner sur-A face of said wall defining means, said insulating portion being so proportioned to permit the ilow of gas evolved from said insulating material by said arc through said arc passage.

18. In an expulsion circuit interruptor, rigid means having a substantially cylindrical passage- Way formed therein for defining the Walls of an arc passage, at least a portion of said wall dening means being lformed of an insulating material which is capable of evolving an arc extinguishing 'gas' when placed in proximity to an electric arc, and a substantially cylindrical plunger movable longitudinally through said arc passage during the operation of said interrupter, said plunger being disposed substantially concentric With said arc passage at all times and having a portion of conducting material for establishing the arc incident to each opening operation of said interrupter'within said arc passage and a portion of insulating material of less cross sectional area, than said arc passage for restrict'- ing the cross-sectional area of saidarc passage, so as to eiect intimate engagement between said arc and the opposed surfaces of said wall delining means and said plunger, saidinsulating por-- tion being so proportioned to permit the ow of gas evolved from said insulating material by said arc through said passage 19. In a circuit interrupter, means for deiining the walls of an arc passage, means for establishing the arc incident to each opening operation oi said interrupter Within said arc passage, a solid member, which is formed at least partially of insulating material, movable into said arc passage to limit the cross-sectional area thereof, means for moving said solid member into said arc passage during theoperation of said interrupter, and a current .responsive means intermediate said movable member and said means for moving that member, said last mentioned the closed circuit position against the biasing force of said spring means, said plunger-having a portion of conducting material movable through said arc chamber during theoperation of said interrupter to establish the arc incident` to each opening operation of said interrupter therein and a portion of insulating material also movable through said arc chamber during each operation of said interruptor, said insulating portion being so proportioned that while it shall substantially restrict the volume of said arc chamber, it shall not completely close that chamber.

21. In an expulsion circuit interrupter, tubular means for dening a closure for said interrupter, means within said closure for deiining an arc chamber and-a spring chamber, said arc chamber being open at least atone end thereof during each opening operation of said interruptor, a plunger arranged for movement through said ar chamber, spring means disposed within said spring chamber which normally biases said plunger to the open circuit position, electro-responsive means which normally retains said plunger in the closed circuit position against the biasing force of said spring means, and means for producing an expulsively flowing blast of gas through said arc chamber during each opening operation of said interruptor, said; plunger having a portion of conducting material movable through said arc chamber to establish the arc incident to each opening operation of said interrupter therein and a portion of insulating material, also movable through said arc chamber during the operation .of said interrupter, to control the physical dimensions of said arc without impeding the free flow of said blast of gas.

22. In an expulsion circuit interrupter, tubular means, at least partially of insulating material, for delining a closure for said interruptor, means within said closure for defining an arc chamber and a. spring chamber, thewalls of said arc chamber being formed, at least in part, of an insulating material which is capable of evolving an Aarc extinguishing gas when placed in proximity to an electric arc and at least one end of said arc chamber being open during each opening operation of said interrupter, a plunger arranged for longitudinal movement through said arc chamber, means including a spring disposed in said spring chamber, which normally biases said plunger to the open circuit position, and electro-responsive means for retaining said plunger in the closed position against the biasing force of said spring means, said plunger having a portion of conducting material for establishing the arc incident to each opening operation of said interrupter within said arc chamber and a portion of insulating material which is so proportioned that it effects intimate engagement between said arc and said gas evolving insulating material and permits the ilow of gas evolved :from said insulating material through said arc pas- S856.

23. In a Acircuit interrupter, means at least partially of .insulating material for defining the Walls of an arc passage, means including a fusible element for establishing an arc in said passage, means along the walls of said passage which gives off a. gas when acted upon by an arc to aid in extinguishing the arc, said wall defining means having an opening for the escape of gas from said passage, and means of insulating material movable into said passage in response to predetermined conditions vfor restricting the passage so that the cross sectional area thereof is smaller than that of the restricting means of insulating material movable therein,

24. In a circuit interrupter, means at least partially' of insulating material for dening the walls of an arc passage, a movable conducting guishing the arc and an insulating member movin said passage, arc contacting the walls of said passage to produce an arc extinguishing gas, means for venting said gas from said passage, and means responsive to the magnitude of arc current for controlling the surface area of said passage adapted to be contacted by said arc to eiectively extinguish arcs of both large and small current magnitude.

26. In a circuit interruptor, means at least partially of insulating material for defining the Walls of an arc passage, means for establishing an arc in said passage, means along the walls of said passage which gives oi a gas when acted upon by an arc to aid in extinguishing the arc, said wall dening means having an opening for venting the gas from said passage, and means movable into said passage -in response to predetermined current conditions for controlling the quantity of arc extinguishing gas emitted by said gas emitting meansrto thereby effectively extinguish arcs `of1both large and small current magnitude.

27. In"a circuit interrupter, means at least partially of insulating material for defining the walls of an arc passage,- movable conducting member for establishing an arc longitudinally of said passage, a material along thewalls of said passage which ,gives off a gas when acted upon by an arc, and an insulating member having a cross sectional area less than that of said pasn sage movable in response to predetermined current conditions by said conducting member into said passage, said passage being provided with venting meansto cause a blast of gas to flow longitudinally of the arc in a direction opposite to the movement'of `said insulating member.

28. In a. circuit interrupter, means at least partially of insulating material for dei'lning the walls of an arc passage, a plunger arranged for movement through said arc passage, said plunger r having a conducting portion normally within said passage and an insulating portion normally without said passage when the plunger is in the closed circuit position, resilient means biasing said plunger to the open circuit position,- a fusible element in circuit with said conducting portion for resilient means being adapted to move said conducting portion through said passage in response to the release thereof by saidy fusible element to establish an arc within said passage and to move sad insulating portion into said passage, said insulating portion having a cross sectional area substantially less than that of said passage.-

V29. In a. circuit interrupter', means defining the walls of an arc passage, means for establishing an arc within said passage, means for venting the products of decomposition of said arc from said passage, means normally positioned without said passage which is movableinto said passage to decrease the volume thereof during the operation of said interrupter, actuating means for said movable means and electro-responsive means for preventing said actuating means from moving said movable means into said arc passage except during the existence of certain predetermined conditions.

30. In a circuit interrupter, means defining the Walls of yan arc passage, means for establishing an arc within said passage, means for venting lthe products of decomposition of said arc from 'retaining'said plunger in the closed circuit position against the bias of said resilient means, said 

